This invention relates to a continuous process for the preparation of aminonaphthalene derivatives.
It is known to prepare derivatives of aminonaphthalenes from the corresponding derivatives of a naphthol and ammonia or amines in an aqueous medium in the presence of a bisulphite according to the so-called Bucherer reaction (Org. Reactions 1, 105 (1942), and Angew. Chem. 79, 329 (1967)).
The Bucherer reaction is generally carried out discontinuously under autogenous pressure at elevated temperature in a closed stirred kettle (Ullmanns Encyclopedia of Industrial Chemistry 7, 995 (1974).
When carrying out the discontinuous process it is a disadvantage that, when the reaction is ended, large amounts of gas and steam, which generally are contaminated with traces of animonaphthalene derivatives, are liberated in a short time. Since these traces of aminonaphthalene derivatives have to be separated off for ecological reasons, an expensive absorption system is necessary. With the continuous procedure, such problems are avoided since the amino-naphthalene derivatives which are not separated off can be recycled into the process.
Stainless steels of the VA type and cast steel are known as materials for apparatus in which the Bucherer reaction can be carried out (Ullmanns Encyclopedia of Industrial Chemistry, 4th edition, volume 7, 396 (1974). These materials are sufficiently resistant to corrosion for carrying out the discontinuous process. However, carrying out the continuous process in apparatus made of the said materials leads to stress corrosion cracking and pitting. The high susceptibility of the known materials to corrosion prevents the continuous process being carried out.